The invention relates to fluid pumps, such as blowers and superchargers for internal combustion engines, and other processes requiring large volumes of fluid at relatively low pressure.
In an internal combustion engine a boost in horsepower can be accomplished by forcing a more dense air/fuel charge into the cylinders with a supercharger. A supercharger can provide a dependable and affordable method of increasing horsepower and torque. A supercharger forces a more dense air/fuel mixture into an internal combustion engine""s cylinders than the engine can draw in under normal conditions. This higher-energy mixture produces more power. Supercharging increases the engine""s volumetric flow without increasing its displacement. Therefore, a supercharged small engine can produce the horsepower and torque of a relatively larger engine.
There are two basic blower systems used to force an air/fuel mixture into an internal combustion engine. These blowers are either a dynamic or a positive displacement equipment. Turbocharging, which is a dynamic process, places a turbine wheel in the exhaust flow of the engine. The turbine blades are directly connected to a centrifugal blower. One major disadvantage of a turbocharger is xe2x80x9cturbo-lag.xe2x80x9d This is the delay that occurs after calling for power with the throttle before the rotational speed of the system spools up to deliver that power. An improperly sized or designed turbo system can rapidly over-boost and damage a spark-ignited internal combustion engine. The sizing of the turbocharger to the engine and the matching of the turbine size and design to impeller size and design are very critical. Additionally, the exhaust turbine tends to cool the exhaust gases thereby delaying the catalyst light-off of modern automotive emissions systems.
Centrifugal impeller-type supercharging is a system having an impeller rotated with a drive belt from the crankshaft. A speed-increaser, either geared or gearless, is required to multiply the speed of the impeller relative to that of the input shaft. The delivery of a centrifugal impeller-type device varies dramatically with its rotational speed, and is prone to under-boost at low speed and over-boost at high speed. An example of a centrifugal impeller supercharger is disclosed by M. Shirai in U.S. Pat. No. 5,158,427.
The most common positive displacement system is the xe2x80x9cRoots blowerxe2x80x9d. In this system, a belt-driven shaft drives two close-clearance rotors which are geared together. Each full rotation sweeps out a specific fixed volume, unlike the fan-like characteristics of a turbine device.
The invention is a fluid pump used as a supercharger to provide an air/fuel mixture to an internal combustion engine in an efficient and reliable manner for sharply increasing the torque and corresponding horsepower of the engine across its entire operating speed range. The supercharger has simple geometric shaped structures which are easy to fabricate at a relatively low cost. The supercharger employs a pair of cooperating rotors that do not have complex curved surfaces which require relatively costly NC profile milling or dedicated machine tool operations. Conventional materials such as aluminum, cast iron or plastics and established fabrication procedures are used to manufacture the supercharger.
The supercharger rotors have clearances relative to their cooperating or mating surfaces and housing surfaces that accommodate deflection. The cylindrical shapes of the rotors and inside surfaces of the housing allow for predictable and repeatable clearances between non-contacting mating parts. This reduces leakage which improves efficiency while maintaining low cost manufacturing procedures. The cylindrical shapes of the supercharger rotors and associated surfaces are inherently rigid and not prone to flexing and twisting when subjected to pressures and inertial loads.
The supercharger has a housing with two generally cylindrical chambers open to each other and fluid inlet and outlet ports. A rotor assembly located in the chambers operates to draw fluid, such as an air/fuel mixture, into the chambers and discharge the fluid out the outlet port and into the intake of an internal combustion engine. The rotor assembly has a pair of rotors mounted on shafts rotatably supported on the housing. Each rotor has semi-cylindrical pockets and semi-cylindrical protrusions that cooperate with the pockets of the adjacent rotor to move fluid through the supercharger when the rotors are rotated. The protrusions on each rotor do not contact the inside cylindrical surfaces of the housing. Also, the protrusions on each rotor do not contact the cooperating rotor as they move into and out of the mating pockets. This allows for both high speed and oil free operation. The protrusions are integral portions of the rotor. The protrusions are located in the semi-cylindrical pockets of the adjacent rotor generally half of the time during rotation of the rotors. Therefore, the pressure fluctuations and associated noise and heat are reduced. There is minimal trapped volume of fluid in the pockets. This reduces one of the common sources of noise, heat, and vibrations among prior devices. Additionally, the fluid inlet has two passages. This improves volumetric efficiency and reduces churning of the fluid and heating of the inlet region of the rotor.